The present invention relates to power systems. More specifically, the present invention relates to a system for managing power in an elevator system from multiple sources based on elevator usage patterns.
Power demand for operating elevators range from positive, in which externally generated power (such as from a power utility) is used, to negative, in which the load in the elevator drives the motor so it produces electricity as a generator. The use of the motor to produce electricity as a generator is commonly called regeneration. In conventional systems, if the regenerated energy is not provided to another component of the elevator system or returned to the utility grid, it is dissipated through a dynamic brake resistor or other electrical load. In this configuration, all demand remains on the power utility to supply power to the elevator system, even during peak power conditions (e.g., when more than one motor starts simultaneously or during periods of high demand). Thus, components of the elevator system that deliver power from the power utility need to be sized to accommodate power demand, which may be more costly and require more space. Also, the regenerated energy that is dissipated is not used, thereby decreasing the efficiency of the power system.
In addition, an elevator drive system is typically designed to operate over a specific input voltage range from a power supply. The components of the drive have voltage and current ratings that allow the drive to continuously operate while the power supply remains within the designated input voltage range. In conventional systems, when the utility voltage sags beyond design limits, the elevator system faults. When a utility power failure occurs or under poor quality conditions in conventional systems, the elevator may become stalled between floors in the elevator hoistway until the power supply returns to normal operation or a mechanic intervenes.